Device for measuring the angle and/or the angular velocity of a rotatable body and/or the torque acting upon said body

ABSTRACT

A device for measuring an angle and/or the torque acting on a rotatable body is proposed according to the invention, whereby the rotational angle is detected by means of magnetic or optical sensors. In particular, in a preferred exemplary embodiment, two devices ( 7, 8 ) are proposed, each of which comprises two optically readable code tracks. The two code tracks ( 1   a,    1   b  or  2   a,    2   b ) on one device ( 7  or  8 ) are similar in design and are offset in relation to each other, so that associated sensors ( 4 ) output a digital signal. The rotational angle is calculated based on the lag between the two digital signals. In a further embodiment it is provided that a torsion element ( 5 ) having a known torsional stiffness is situated between the two devices ( 7, 8 ). Torque transferred by the rotatable body ( 3 ) can also be calculated therefore from the angular difference of the two devices  7, 8.  The device is used preferably in the steering axle of a motor vehicle.

BACKGROUND OF THE INVENTION

[0001] The invention concerns in general a device for measuring theangle and/or angular velocity of a rotatable body, and, in particular, adevice for measuring the angle and/or angular velocity of a rotatablebody and/or of the torque acting on it.

[0002] A very exact determination of a rotational angle is necessary formany systems, e.g., in the automotive industry. A specific applicationof such a device is a steering-wheel angle sensor, whereby enormoussafety requirements exist.

[0003] A device is made known in DE-A-195 06 938 belonging to theapplicant, which said device is used to measure the angle and/or theangular velocity of the rotatable body, in particular a body that can berotated by more than 360°, according to the preamble of claim 1. In thecase of the known device, the first and second devices are each formedout of a toothed wheel with associated angle sensor, whereby the twotoothed wheels—when the numbers of teeth are different—are in mesh withone toothed wheel that is mounted on the steering-wheel shaft. Using amodified vernier method, the angle of the steering axle can therefore bedetermined from the current angular and/or phase difference between thetwo toothed wheels. This device therefore offers the advantage thatmultiple rotations can be detected, but it is disadvantageous in thatthe detection takes place by means of the interconnection of toothedwheels and therefore not in a contactless manner. Moreover, theinstallation space required for such a device is relatively large,making it difficult to integrate it, particularly on the steering axle,where the multi-function switches are also accommodated. Finally, alaborious evaluation using an arc tangent method is required to measurethe individual rotational angles.

[0004] Furthermore, diverse angle sensors are known that are based oncontactless detection. They are generally not suited to measuring angleswith great accuracy. These devices and methods also require expensiveevaluation circuits and algorithms or, alternatively, they haveinsufficient accuracy or an insufficient measuring range if the deviceis suited only for use with small angles, for example.

[0005] There is a need, therefore, for an improved device for measuringthe angle and/or the angular velocity of a rotatable body and of thetorque acting on it. It is an object of the present invention to furtherdevelop a generic device—as was made known in DE-A-195 06 939, forexample—having at least first and second devices that output differentsignals to an evaluation circuit in response to a rotation of the bodyin such a fashion that it takes up very little space and makes a simpleevaluation and determination of the angle possible, whereby thedetection is to take place in contactless fashion overall.

[0006] This object is attained according to the invention by means of adevice having the features in claim 1. Preferred exemplary embodimentsare defined in the dependent claims.

[0007] In particular, the invention proposes that, in the case of thegeneric device, a field-producing and/or field-changing arrangement oran arrangement that responds to the field is associated with therotatable body and the stationary part of the device as a component ofevery device. In this fashion, every one of the devices that respondsdifferently to a rotation of the body provides an output signal that canbe detected in contactless fashion. Once the angle is measured directlyat the rotatable body, the error influence—resulting from the tolerancesof toothed wheels used so far—can be avoided. Low-noise operation thatis free from wear is advantageous.

[0008] Advantageously, the arrangement responding to the field cancontain a field-producing and/or field-changing arrangement, by way ofwhich the mutually-influencing or mutually-influenced fields can beevaluated in order to obtain the rotational angle to be measured.

[0009] In order to obtain an insensitivity to fluctuations in the spacebetween the components of the devices, it is preferred that at least onefield flux concentrating element is provided, in particular to formclosed field lines. In this fashion, tolerances and time-induced changesin fields can also be handled more easily, which makes the width of thepole-face arc non-critical when magnets are used.

[0010] Advantageously, at least one of the field-producing and/orfield-changing arrangements provides a periodically changing field, inparticular an electrical and/or magnetic field. When a periodicallychanging field is involved, the detection accuracy can be increased bymeans of an appropriate design of the sensors, whereby minimal angularincrements in particular can be determined with greater accuracy bymeans of a periodically changing magnetic field. In general, theaccuracy increases with the number of pole pairs.

[0011] In the case of a preferred exemplary embodiment, at least one ofthe field-producing and/or field-changing arrangements is designedextending around the periphery in relation to the rotatable body, inparticular located on said rotatable body or integrated in it. Thispreferred exemplary embodiment makes a device possible that requiresonly a minimal amount of space, so that it can be used easily as asteering angular sensor.

[0012] At least one of the field-producing and/or field-changingarrangements can form a radial field, e.g., a magnetic field, electricalfield, or an electromagnetic field. In this case, the sensors could beprovided radially in relation to the rotating body.

[0013] As an alternative, it is also possible that at least one of thefield-producing and/or field-changing arrangements forms an axial field,whereby a corresponding positioning of the detection sensors is to becarried out.

[0014] Advantageously, at least two field-producing and/orfield-changing arrangements are provided that form different fields, inparticular defining a different number of field poles, whereby, inparticular, this said number of field poles can differ by one. Byproviding two field-producing and/or field-changing arrangements, acomplete decoupling can take place, in particular when two separatedetection arrangements are formed at appropriate locations.

[0015] In a preferred exemplary embodiment, at least one of thefield-producing and/or field-changing arrangements is designed as amulti-pole wheel or a multi-pole ring. A multi-pole wheel or ring is anarrangement of poles that comprises, in alternating fashion, inversepoles, or they also contain, in alternating fashion, field-producing andnon-field-producing or field-influencing and non-field-influencingportions.

[0016] The field-changing arrangement can advantageously have the shapeof a punched, slotted, or perforated disk, or a punched, slotted, orperforated ring, independently of whether radial or axial fields areused.

[0017] So that each of the devices provides an output signal that is aseasy to evaluate as possible and is as linear as possible, at least oneof the arrangements responding to the field can contain two fieldsensors that deliver sinusoidal or asinusoidal output signals,separated, in particular, by a quarter period of the periodic fieldformed by the corresponding field-producing and/or field-changingarrangement. As described above, the field can be an electrical field, amagnetic field, or any electromagnetic field.

[0018] Advantageously, the sensors in this case are connected in abridge circuit, in particular a Wheatstone bridge circuit, and theyoutput their signals to said circuits. When the bridge circuit is used,subtraction can be performed. When elements having a linearcharacteristic as well are used, the respective, outputted angular valuecan be determined directly without using a complex arc tangentprocedure.

[0019] In the case of a particularly preferred exemplary embodiment,each sensor of a device is connected in a partial-bridge circuit, inparticular a half-bridge of the bridge circuit.

[0020] Finally, it is preferred that the device according to theinvention is used as a steering-wheel angular sensor, and at least twofield-producing and/or field-changing arrangements are assigned to thesteering shaft as field-pole code tracks, in particular magnetic codetracks.

[0021] An alternative exemplary embodiment—that is essential to theinvention in terms of measuring an angle and/or torque—is provided thatdetects a rotational body opposite to the fixed sensors using first andsecond optical devices. It is considered to be particularly advantageousthat the optical devices are attached to the rotatable body—the steeringaxle of a motor vehicle in this case. The two devices substantiallycomprise two optically readable code tracks, whereby each code track isassociated with an optical sensor. The advantage of optical sampling isthe fact that the beams of light are easier to detect and they cannot beinfluenced by electromagnetic interference fields. Additionally, theoptically-readable signal can be converted to an electrical signal veryeasily using a photo-sensor. It is also advantageous that a digitaloutput signal is obtained by means of the optical sampling, based onwhich digital output signal the angle or angular changes can bedetermined with a high degree of accuracy and a high degree ofinsensitivity to contamination.

[0022] Advantageous further developments and improvements of the devicedescribed in the main claim are made possible by means of the measureslisted in the dependent claims. In particular, the code signal isdetected in digital and analog form by means of a plurality ofoptically-readable markings, so that the rotational angle can bedetermined using simple phase comparison between associated code tracks.

[0023] It is also favorable that the fields of the markings can bedifferentiated in terms of their light intensity, color, and/or size. Inthe case of adjacent light-dark fields in particular, unambiguouslight-dark transitions occur that can be detected based on the steepvoltage jump of the electrical signal. An unambiguous delineationtherefore results, which is largely immune to interference.

[0024] The contrast between the light-dark fields and at the light-darktransitions can be improved even further by illuminating the markingsusing a light source. In the case of tracks on one device that have anidentical design, this results in two different signal sequences; thismakes it particularly easy to determine the angle, e.g., using aclassical or modified vernier method. For this purpose, the number ofmarkings of adjacent tracks on one device are advantageously selected tobe different, in order to obtain a phase displacement that is changeablearound the circumference of the axis of rotation.

[0025] When an appropriate number of markings on a track is selected andwhen the markings are designed appropriately, the vernier method and, inparticular, the modified vernier method, can be used to measure theangle. The measuring accuracy is advantageously increased by correctingthe results of the measurements from the code tracks anew using themodified vernier method.

[0026] In cases where torque is to be determined as well, a torsionelement having a known torsional stiffness is used between the twodevices. If the rotational angle of the first as well as the seconddevice is then measured, then the torque can be advantageouslydetermined from the difference of the two angles and the known torsionalstiffness. In this fashion, two variables can be measured simultaneouslyusing the device according to the invention.

[0027] The markings of the two devices are preferably selected so thatthe classical or modified vernier method can be applied anew to therespective measured results. This increases the measuring accuracyand/or the measuring range of the device without requiring additionaldevices.

[0028] In order to protect the optical devices from potential risk ofcontamination in the motor vehicle, an enclosing metal-cladding for thedevice appears to be particularly advantageous.

[0029] An advantageous application of the device is seen in the case ofa steering axle of a motor vehicle, in order to measure the rotationalangle and/or the torque. These variables can be used for further vehiclefunctions that are required, for example, to determine the dynamicvehicle stability, and to support the steering effort and/or navigation.

[0030] In summary it can be stated that, with the means of achieving theobject, according to the invention, a simple detection of angles and/orangular velocities of a rotatable body is given that also includesmeasurement of torque, whereby the evaluation circuit can be designedsimple in nature, and the space required to implement the device is verysmall.

[0031] Further advantages and features of the present invention resultfrom the following—purely exemplary—description of a few preferredexemplary embodiments, whereby the description makes reference to theattached drawings.

[0032]FIG. 1 shows a steering-wheel angular sensor according to a firstpreferred exemplary embodiment of the invention in a systematic view(FIG. 1A), in a tangential side view (FIG. 1B), and in radial side viewsat different angular positions (FIGS. 1C and 1D).

[0033]FIG. 2 shows a variant of the exemplary embodiment shown in FIG. 1in corresponding representation, whereby field-changing devices areimplemented in this case, as opposed to the field-producing devices usedin FIG. 1.

[0034]FIG. 3 shows a further steering-wheel angular sensor device as thethird preferred exemplary embodiment of the device according to theinvention, in which a radial field is used instead of the axial fieldused in FIGS. 1 and 2.

[0035]FIG. 4 shows a variant of the embodiment shown in FIG. 3, whereby,as in FIG. 2, field-changing devices are used instead of field-producingdevices.

[0036]FIG. 5 shows a further variant of the embodiment shown in FIG. 3in different angular positions (FIG. 5A, FIG. 5B), whereby afield-producing arrangement functions as the field-changing arrangement.

[0037]FIG. 6 is a schematic view of the position detection in the caseof the exemplary embodiment shown in FIG. 5 using field fluxconcentrating elements.

[0038]FIG. 7 shows an exemplary embodiment of a combinationsteering-angle/steering-torque sensor (schematically).

[0039]FIG. 8 shows a further exemplary embodiment of a combinationsteering-angle/steering-torque sensor (schematically).

[0040]FIG. 9 shows various designs of sensors according to FIG. 7 or 8,whereby a plurality of sensors per magnetic track can also be presentfor the purpose of averaging.

[0041]FIG. 10 shows the evaluation of the signals from a combinationsteering-angle/steering-torque sensor.

[0042]FIG. 11 shows an optical device having two stacked opticaldevices, each of which has two code tracks and four sensors.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] In the following description, reference is largely madeexclusively to magnetic fields and, in the case of the exemplaryembodiment shown in FIG. 4, reference is made to an electrical field;one skilled in the art should recognize, however, that randomcombinations, i.e., any electromagnetic fields, can be used. Forexample, light diodes could be used as field poles instead of magnets,the emitted field of which can be detected using appropriateopto-electronic sensors.

[0044] The exemplary embodiment shown in FIG. 1 includes a disk mountedon the steering axle 10, on which disk code tracks 20, 22 are provided.Each of the code tracks 20, 22 comprises a plurality of alternatinglyarranged permanent magnets, as indicated by the arrows pointing indifferent directions. The two code tracks 20, 22 are distributeddifferently, whereby it is particularly advantageous for the smallestpossible difference to exist, e.g., a difference of only one pole pair.In the exemplary embodiment shown, one of the tracks 20, 22 contains aspacing of n pole pairs, while the other has a spacing of n+1 polepairs. When the rotatable body 10 rotates—the steering axle in thiscase—the code tracks 20, 22 are therefore rotated by a correspondingangle in the exemplary embodiment shown. Sensor arrangements 12 and 14are provided on a fixed part of the device over each of the code tracks20, 22. Using the sensor arrangement 12, 14, the relative position ofthe magnetic code track 20 or 22 lying under it can be detected.

[0045] The detected sensor elements can be measuring elements thatproduce conventional sinusoidal/cosinusoidal signals, such as AMR-,GMR-Hall sensors. The evaluation algorithm can be carried out accordingto the arc tangent method.

[0046] In the case of the exemplary embodiment shown, each of the sensorarrangements 12, 14 comprises two sensors 12 a, 12 b or 14 a, 14 b. Thesensors 12 a and 12 b or 14 a and 14 b provided in pairs in each caseare advantageously separated by a quarter or eighth period of theperiodically changing magnetic field formed by the code tracks 20, 22.Such a separation makes it possible to connect the sensors ashalf-bridge of a Wheatstone bridge circuit in each case, so that asimple evaluation circuit can be realized, because subtraction isperformed on the one hand and, on the other, a nearly linear anglesignal that can be evaluated directly is provided when elements are usedhaving substantially linear characteristics.

[0047] The angular positions detected therewith can be referencedagainst each other, so that, when the generally known vernier method or,better, when a modified vernier method, or a combination of the two isused, the real angle of the rotatable body 10 can be determined. Theexpanded vernier method is described in the publication DE-A-195 06 938,so this procedure need not be described in further detail.

[0048] Although the field-producing portions of a respective device moveon the exemplary embodiment shown, one skilled in the art will recognizethat a corresponding reversal is also feasible, in which the sensorarrangements move with the rotatable body, while the code tracks areprovided fixed in position around the rotatable body.

[0049] The particularly advantageous distance between two sensors 12 a,12 b or 14 a, 14 b is shown in detail in the tangential sectional viewin FIG. 1B.

[0050] Finally, one can see, in the sectional views in FIGS. 1C and D,how the respective code tracks are present in different positions withregard for the sensor arrangements at different angles of the rotatingbody.

[0051] In the case of the exemplary embodiment shown in FIG. 2, afield-changing device is used instead of the magnetic tracks, which saidfield-changing device also defines code tracks 24, 26. The mode ofaction and the general construction is similar to FIG. 1, so thedescription will not be repeated here. It is to be mentioned, however,that, in the exemplary embodiment shown, a stationary permanent magnet28 is positioned underneath the disk, which said disk moves with therotatable body 10 and contains code tracks 24, 26. In the exemplaryembodiment shown, the code tracks are formed by means of simplerecesses, but one skilled in the art should recognize that the mostdiverse possibilities can be used here. It would be feasible, forexample, to provide regions having a different magnetic permeabilityinstead of the simple recesses. When fields other than magnetic fieldsare used, a corresponding design would be feasible with considerationfor different dielectric properties, optical properties, or combinationdielectric and magnetic permeability properties.

[0052] A further exemplary embodiment of the device according to theinvention is shown in FIG. 3, in which the code tracks 20, 22 are notarranged on a disk, but rather are integrated directly in the steeringaxle 10. The code tracks therefore provide a radially periodicallychanging field that can be detected using appropriately situated sensorarrangements 12, 14. The evaluation is carried out as it is with thepreceding exemplary embodiments using the vernier method, so that theexisting phase difference between the detection signals can be used todetermine the overall rotational angle of the steering axle. Everysensor arrangement 12, 14 also comprises two sensors that are separatedby a quarter period λ/4 of the changing field, in order to make a simpleevaluation possible.

[0053] Shown in FIG. 4 is a further preferred exemplary embodiment ofthe device according to the invention that basically combines theprinciples of the exemplary embodiments presented in FIGS. 2 and 3. Inthe case of this exemplary embodiment, the rotating body 10 is designedas a hollow tube, in the middle of which a simple current-carrying wireor an optical waveguide—as the field-producing device—can be arranged.The rotating body 10 contains two rings having recesses that form codetracks 24, 26 as described hereinabove. As is the case with the otherexemplary embodiments described previously, each of the code tracksshould comprise a different spacing, in particular a spacing thatdiffers by one, i.e., one of the code tracks should comprise a number of“n” openings, while the other should comprise a number of “n+1”openings. The sensors are arranged in accordance with the exemplaryembodiment in FIG. 3, in order to detect the changing field in each caseabove a respective track 24, 26 when the rotating body 10 rotates. Theentire rotational angle is determined from the difference—in particular,the phase difference of two signals—in the usual manner by means of anevaluation circuit and the vernier method.

[0054]FIGS. 5a and 5 b show a schematic view of one of the first andsecond devices that output different signals to a not shown evaluationcircuit in response to the rotation of the body 10. In the case of theexemplary embodiment shown here, annular magnet multi-pole wheels 20, 22and 24, 26 are used in similar fashion as with the exemplary embodimentshown in FIG. 3, whereby the inner multi-pole ring is interconnectedwith the rotating body 10, as in the preceding exemplary embodiments.The outer magnet pole ring 24, 26 is designed rotatable in nature inrelation to the rotatable body 10 and the inner magnet pole ring 20, 22,so that a periodically changing, reciprocal influence of the respectivefields that are formed results. In the case of the position shown inFIG. 5a, respective magnet poles oppose each other in such a fashionthat the fields essentially cancel each other out. In the angularposition shown in FIG. 5b, the poles are arranged in such a fashion thatthe respective field strengths add up.

[0055]FIGS. 6a and 6 b show views of a field evaluation device as afurther component of the arrangement responding to the field, which saidfield evaluation device includes two Hall sensors 12, 14 in front. Thefields produced by the multi-pole rings shown in FIG. 5 are directed tothe Hall sensors 12, 14 by field conducting elements 32, 34, 36. As oneskilled in the art will recognize in the views shown in FIGS. 6a, 6 b,an upper flux concentrating piece 32 is provided that guides field linesin the transition area between the two multi-pole rings 20, 22 and 24,26 toward one of the Hall sensors. As shown in FIG. 5a, closed fieldlines are therefore formed in the upper portion when the pole positionsare anti-parallel, whereby a tee 36 is provided as a further fluxconcentrating piece behind the upper Hall sensor 12, 14. After therotatable body is rotated toward a position in which the poles of themulti-pole rings are parallel—as shown in FIG. 5b—the field lines areclosed by the lower flux concentrating piece 34 and the tee 36, wherebya further Hall sensor is situated between the tee 36 and the lower fluxconcentrating piece 34. By providing two Hall sensors in the mannershown, and by using a principle of differences, insensitivity totemperature fluctuations and ageing can be obtained, because the outputsignal can be standardized against the total flux. One skilled in theart should recognize, however, that this subtraction is purely optional.As is the case with the preceding exemplary embodiments as well, aportal to any fields other than magnetic fields can be provided.

[0056] In summary, it can be stated that the device according to theinvention makes it possible to determine the angle of the rotatable bodyexactly and simply, and no contact, e.g., by toothed wheels or the like,is necessary. In other words, a simple and exact angle measurement orangular velocity measurement takes place in a contactless manner usingsimple, known components which—as mentioned hereinabove—shouldadvantageously contain elements having a linear characteristic. Thedifferent adaptations to different field-producing and/orfield-influencing devices should be common knowledge to one skilled inthe art and therefore need not be described here in any greater detail.Once moveable parts can be eliminated entirely, the device according tothe invention is particularly suited for use as a steering-wheel angularsensor, in particular since a high degree of measuring accuracy is givenwhile requiring only minimal installation space.

[0057] Although the present invention was described hereinabovecompletely and in detail with reference to purely illustrative exemplaryembodiments preferred at this time, one skilled in the art shouldrecognize that the most diverse modifications are possible within thescope of protection defined by the claims. In particular, one skilled inthe art should recognize that individual features of an exemplaryembodiment can be combined in any fashion with other features of otherexemplary embodiments. In this context it would also be feasible, forexample, to provide one of the code tracks according to an arrangementof FIG. 4 or 5, while the other code track is provided in accordancewith a design according to FIG. 1 or 2.

[0058] Various exemplary embodiments of combinationsteering-angle/steering-torque sensors, including the associatedevaluation procedure, are shown in FIGS. 7 through 11. The multi-polewheels are read in each case by sensor elements that deliversinusoidal/cosinusoidal signals. The evaluation of the output signalsfrom the sensor elements takes place according to the modified verniermethod, about which the following is to be noted:

[0059] Transfer of the modified vernier principle to the circumstancesdescribed (FIG. 1e):

[0060] Determination of φ:$\phi = {\alpha + {i\frac{360^{{^\circ}}}{n + 1}}}$ $\begin{matrix}{n:{{number}\quad {of}\quad {pole}\quad {pairs}}} \\{\alpha,\quad {\beta:{{measured}\quad {values}\quad {of}\quad {sensors}}}} \\{i,\quad {j:{unknown}}}\end{matrix}\quad$ $\phi = {\beta + {j\frac{360^{{^\circ}}}{n}}}$

[0061] Equate and transform:${\frac{\alpha + \beta}{360^{{^\circ}}}*n*\left( {n + 1} \right)} = {{{j*\left( {n + 1} \right)} - {i*n}} = {{{whole}\quad {number},\quad {with}\quad i} = {j = k}}}$

[0062] Therefore: $\begin{matrix}{{{\frac{\alpha + \beta}{360^{{^\circ}}}{n\left( {n + 1} \right)}} = {k,\quad {with}\quad k{\quad \quad}{being}\quad a\quad {whole}\quad {number},}}\quad} \\{\phi = {\frac{\left( {\alpha + \beta} \right)}{2} + {k*180^{{^\circ}}*\left( {{1/\left( {n + 1} \right)} + {1/n}} \right)}}}\end{matrix}\quad$

[0063] Errors that make their way into the evaluation can be reducedusing special correction procedures in which principles of the classicaland/or the modified vernier principle are taken into account.

[0064] In addition to the angle, the acting torque, e.g., the steeringtorque, can also be determined using the sensors according to FIGS. 7and 8.

[0065] The acting torque during the steering procedure causes thetorsion bar integrated in the steering column to twist. The upper endrotates in relation to the lower end by a maximum of +/−5°, for example.In order to measure the torque, this relative rotational angle—the“torsional angle”—must be measured. There are two ways to do this: theabsolute steering angle of the upper and lower ends of the torsion barare each determined using the method described under point 1). Thedifference between the two angles equals the torsional angle. Or, it canbe measured directly via the relative displacement of twoidentically-coded pole wheels, one of which is situated at the top ofthe torsion bar, and the other of which is situated at the bottom of thetorsion bar. A minimum of three pole wheels are needed for this. Thesepossible methods are presented in summary form in FIG. 9.

[0066] Various Exemplary Embodiments

[0067] Pole wheel combinations: Each pole wheel can thereby be regardedas a magnetic code track as well.

[0068] Steering angle determination using

[0069] two pole wheels, the pole pair number of which is relativelyprime, e.g., with n and n+1 pole pairs; they can also be situated as twocode tracks on one pole wheel;

[0070] three pole wheels with n−1, n and n+1 pole pairs. Thiscombination increases the accuracy, while simultaneously creatingredundancy. It is expandable to include more pole wheels withcorresponding pole pair numbers;

[0071] Addition of a “three-poled” pole wheel for differentiation ofarea when sensor elements are used that have ranges of unambiguousnessof less than 360°;

[0072] Expand the measuring range by a pole wheel number>2.

[0073] Determine the steering torque

[0074] by calculating the absolute difference

[0075] by measuring the relative angle of identically-coded pole wheels

[0076] For the exemplary embodiment shown in FIG. 8, a detaileddescription will now be provided as to how the absolute angle and thetorque can be measured simultaneously using the same measuring principleand a minimal number of sensors and assemblies. The two variables aredetermined in contactless fashion, and self-diagnosis is possible.Access by different systems, such as via a CAN bus (Controller AreaNetwork) is possible.

[0077] The proposal is based, for example, on the simultaneousmeasurement of the steering angle and the steering torque. A magneticmeasuring method is presented as the measuring principle. The proposalis not limited to this magnetic method, however. Any principle—optical,eddy current, inductive, . . . —that is based on analogsinusoidal-cosinusoidal signals can be used.

[0078] As illustrated in FIG. 7, a torsion bar is built into thesteering system in order to measure the rotational angle and torque. Twomulti-pole rings with M and M+X magnetic poles are situated on the oneend of the torsion bar. A third multi-pole ring having N magnetic polesis situated at the other end. A sensor (AMR, Hall, GMR, magnetoresistor)is located over each ring. Each sensor delivers a sinusoidal signal anda cosinusoidal signal that is a function of the mechanical angle.

[0079] Measuring the Steering Angle

[0080] The multi-pole rings and sensors located on one end are used tomeasure the steering angle. If X=2, the absolute angle can be determinedusing the modified vernier method. This method is to be used here, andthe absolute angle is calculated with the signals S1 (U sin(1), Ucos(1)), and S2 (U sin(2), U cos(2)).

[0081] Measuring the Torque

[0082] The torque is measured via the angular difference. The torque isproportional to the angular difference in the elastic measuring range ofthe torsion element. The angular difference is determined via the twosignals S1 (U sin(1), U cos (1)) and S3 (U sin(3), U cos(3)) at thetorsion ends.

[0083] The sensor delivers two signals:

U sin(1)=A1*sin(w1)+O sin(1)

U cos(1)=A1*cos(w1)+O cos(1)

[0084] Sensor 3 also delivers two signals:

[0085] ti U sin(3)=A3*sin(w3)+O sin(3)

U cos(3)=A3*cos(w3)+O cos(3)

[0086] Whereby U represents the electrical signals at the respectivemechanical angle w. A represents amplitudes, and O represents the offsetvalues of the sensors. By means of the mechanical rotation, theamplitudes and offsets of the four signals can be determined from maximaand minima. An alternative method for offset determination and offsetcompensation was demonstrated in DE-P 199 28482. The corrected signalsU# are purged of offset. $\begin{matrix}{{U\# {\sin (1)}} = {{{U\quad {\sin (1)}} - {O\quad {\sin (1)}}} = {{A1}*{\sin ({w1})}}}} \\{{U\# {\cos (1)}} = {{{U\quad {\cos (1)}} - {O\quad {\cos (1)}}} = {{A1}*{\cos ({w1})}}}} \\{{U\# {\sin (3)}} = {{{U\quad {\sin (3)}} - {O\quad {\sin (3)}}} = {{A3}*{\sin ({w3})}}}} \\{{U\# {\cos (3)}} = {{{U\quad {\cos (3)}} - {O\quad {\cos (3)}}} = {{A3}*{\cos ({w3})}}}}\end{matrix}$

[0087] The angular difference w1−w3 is the result that is sought.

[0088] Using analog electronic operations (multiplication, subtraction,comparation), or by processing at the digital level, the difference canbe determined as follows:U#sin (1) * U#cos (3) − U#cos (1) * U#sin (3) = A1 * sin (w1) * A3 * cos (w3) − A1 * cos (w1) * A3 * sin (w3) = A1 * A3 * sin (w1 − w3)

[0089] The following applies for small angles: sin(w1−w3)=w1−w3

[0090] with 0.1% relative error in the angular interval (−4.4° to +4.4°)in degrees or (−0.077 to −0.077) in rad.

[0091] The angular difference, therefore, is:w1 − w3 = (U#sin (1) * U#cos (3) − U#cos (1) * U#sin (3)/(A1 * A3)

[0092] This evaluation method is very sensitive to the smallest angulardifferences. Using the procedure described above, the torque can bedetermined directly from the angular difference. Another starting pointwould be to adjust the difference to zero using a closed loop. Thecontrolled variable would be equal to the angular difference.

[0093] Remarks:

[0094] 1) Another combination of signals is possible as well; theyshould also lead to a sine of the angular difference.

[0095] 2) The angular difference could also be obtained by means of thedifference between two absolute angle sensors. This would require 4sensors and 4 multi-pole rings, and the method would place requirementson the absolute angular measurements that are too high. In this case,the difference of two large angle values is obtained.

[0096] Self-Diagnosis

[0097] Absolute angle: For the absolute angle, the known method of themodified vernier principle is used. Tracking the whole-number k(allowed/not allowed) jumps makes it possible to detect errors andimplement a line-of-retreat strategy.

[0098] Torque:

[0099] If the angular difference exceeds the maximum permissible range,e.g., +/−4°, an error message is output. If overload occurs, forexample, the system stops intervening.

[0100] The new difference to be calculated (U# cos(1)*U# cos(3)+U#sin(1)* U# sin(3))/(A1*A3) must not deviate from 1 by more than 0.5%(cos{circumflex over ( )}2 (4°)=0.995.

[0101] Another alternative would be to check the expression (U#sin(3)*U#sin(3)+U# cos(3)*U# cos(3))/(A3*A3)* for a deviation from 1 of0.5%. At the same time, the whole number k must not perform anyunpermitted jumps.

[0102] The device in particular for contactless and optical measurementof an angle and/or torque according to FIG. 12 will be described ingreater detail hereinbelow. As illustrated in FIG. 12, the two devices 7and 8 are situated on one rotatable body 3. The rotatable body 3 ispreferrably designed as a steering axle in a motor vehicle and comprisesa torsion element 5 with which the torque acting on the steering axle 3can be measured. The two devices 7, 8 are situated on both ends of thetorsion element 5, so that, when the torque acts on the torsion element5, a different rotational angle than the angular difference Θ−ψ can bemeasured.

[0103] The two devices 7, 8 each comprise two code tracks 1 a, 1 b or 2a, 2 b. The code tracks are designed equal in nature with regard for thewidth of their adjacent fields, but they have a different number ofmarkings 9 around their circumference. For example, the code track 1 ahas 45 markings 9, the code track 1 b has 50 markings 9, code track 2 ahas 44 markings 9, and code track 2 b has 48 markings 9 distributedaround their circumferences. In an alternative exemplary embodiment ofthe invention, it is provided to provide a multiple of these markings 9around the circumference. Two adjacent markings or fields 9 in each casediffer in terms of their light intensity, color and/or size. They arepreferably designed as light-dark fields, so that sharp andhigh-contrast light-dark transitions result. To increase the contrast,light fixtures 6 are provided that are associated with the devices 7, 8in such a fashion that they shed the light reflected by the markings 9into associated sensors 4. As further illustrated in FIG. 12, a sensor 4is assigned to each code track 1 a, 1 b, 2 a, 2 b, which said sensoressentially receives only the light reflected from the associated codetrack. The sensor 4 converts the light signal received into uniformelectrical signals, which can be picked off as a digital signal S1 a, S1b, S2 a and S2 b at the output of the sensors 4, and are directed to anot shown evaluation circuit.

[0104] An aspect that is considered essential to the invention is thefact that the markings 9 of the code tracks 1 a, 1 b or 2 a, 2 b aredesigned uniform in nature. In each case, both code tracks 1 a, 1 b or 2a, 2 b of the devices 7 or 8 are coordinated with each other exactly andcomprise a relative phase offset. This phase offset is also reflected inthe electrical signal S1 a, S1 b, S2 a, S2 b, as illustrated in FIG. 12using the dashed lines. The offset, therefore, becomes increasinglygreater from one pulse to the next pulse as the rotational angleincreases, so that this difference is evaluated using a standard or, inparticular, the known, modified vernier method, which was also madeknown in DE 195 06 938 A1.

[0105] It should be noted that the smallest unit of a marking 9 isdetermined in particular by means of the light-dark transition. Thegreater the contrast of these transitions, the lower the sensitivity todisturbance, and the likelihood that measuring errors will occur. Tolower the susceptibility to interference, an enclosing metal-cladding 10is preferably provided, which encloses the rotatable body 3 with thegreatest sealing effect possible.

[0106] As described previously, 44 to 50 markings 9 were selected foreach of the four code tracks 1 a, 1 b, 2 a and 2 b in order to obtain ahigh level of measuring accuracy and angle resolution for the rotationalangle using the modified vernier method, if possible. When the markings9 are selected in this manner, the measured values from the tracks 1 a,1 b repeat five times per circumference and, in the case of the tracks 2a, 2 b, they repeat four times per circumference. If these measuredvalues undergo the modified vernier method anew, a measured valueresults that is unambiguous around the entire circumference (2 π). Ahigh resolution for the angle is therefore obtained, which results fromthe high dividend. At the same time, a range of unambiguousness of onefull rotation is obtained. The modified vernier method makes it possiblefor an angular difference to be present between the first code tracks 1a, 1 b and the second code tracks 2 a, 2 b without diminishing theaccuracy. This angular difference can also result from the rotation ofthe torsion bar 5, for example. If the angular difference Θ−ψ ismeasured in accordance with the two devices 7, 8, then the torquetransferred by the steering axle 3 can be determined in addition to thetorque when the torsional stiffness of the torsion element 5 is known.

[0107] In an alternative embodiment of the invention, one or morefurther optical code tracks of a third device are feasible, of the typedescribed hereinabove in conjunction with the magnetic devices.

What is claimed is:
 1. A device for measuring an angle and/or the torqueof a rotatable body (3) having at least first (4, 6, 7) and second (4,6, 8) devices that output different signals to an evaluation circuit inresponse to a rotation of the body (3), wherein the two devices (4, 6,7, 8) each comprise two optically-readable code tracks (1 a, 1 b or 2 a,2 b), wherein one optical sensor (4) is assigned to each code track (1a, 1 b or 2 a, 2 b), and wherein each optical sensor (4) is designed todetect only the signals from the assigned code track (1 a, 1 b or 2 a, 2b), and to send their information as electrical signals to theevaluation circuit.
 2. The device according to claim 1, wherein one codetrack (1 a, 1 b or 2 a, 2 b) comprises numerous optically detectablemarkings (9).
 3. The device according to claim 2, wherein the markings(9) comprise fields that differ in terms of light intensity, colorand/or size.
 4. The device according to claim 2 or 3, wherein themarkings (9) comprise light-dark fields that alternate with light-darktransitions.
 5. The device according to one of the preceding claims,wherein the markings (9) can be illuminated by a light source (6). 6.The device according to one of the preceding claims, wherein the twocode tracks (1 a, 1 b or 2 a, 2 b) of one device (7, 8) comprisemarkings (9) having the same design.
 7. The device according to one ofthe preceding claims, wherein the number of markings (9) distributedaround the circumference differs.
 8. The device according to claim 7,wherein the number of markings (9) is selected so that, in particular, avernier method or a modified vernier method can be used to measure theangle.
 9. The device according to claim 7 or 8, wherein the markings (9)are designed so that the modified vernier method can be used anew on theresults of the measurements of the code tracks (1 a, 1 b or 2 a, 2 b).10. The device according to one of the preceding claims, wherein atorsion element (5) having a known torsional stiffness is switchablebetween the two devices (7, 8).
 11. The device according to claim 10,wherein torque can be measured based on an offset angle between the twodevices (7, 8).
 12. The device according to one of the preceding claims,wherein at least one further code track can be provided.
 13. The deviceaccording to one of the preceding claims, wherein an enclosingmetal-cladding (10) for the device can be provided, which saidmetal-cladding protects the devices (4, 6, 7, 8) extensively againstcontamination.
 14. The device according to one of the preceding claimsto use on a steering axle (3) of a motor vehicle.